Electrical heating units of the sheathed type have been extensively utilized from many years. In units of this type, a resistance-type conductor is enclosed by a metal sheath and embedded in a compacted mass of granular insulating material, such as magnesium oxide. The ends of the sheath are closed in any suitable way, as by swaging or rolling. The terminals formed by the ends of the conductor project out from the sheath so that suitable external electrical connection can be made thereto. Such sheathed heating units are utilized in a large variety of electrical appliances, such as ranges, cooking devices and the like.
Such sheathed heating elements have long presented a manufacturing problem in that automating the manufacturing technique to permit efficient mass production has met with limited and questionable success. Thus, sheathed heating elements are still manufactured by techniques which involve a large number of manual operations. This makes the manufacturing of these elements expensive, and results in greater manufacturing variations in the finished elements.
In an attempt to at least partially automate the manufacture of sheathed heating elements, so as to both permit the mass manufacture of same while maintaining a more uniform construction, there has been developed the apparatus disclosed in U.S. Pat. No. 2,973,572 issued to S. A. Oakley. While the Oakley apparatus does permit a substantial improvement in the manufacture of sheathed heating elements, nevertheless this apparatus also possesses features which have been less than optimum. For example, it is desirable to fill and manufacture such sheathed elements at a rate greater than that permitted by the Oakley apparatus, and it is also desirable to provide an improved apparatus which permits handling of the components of the sheathed heating element in a different manner to permit a more efficient and simpler manufacturing process.
Accordingly, it is an object of the present invention to provide an apparatus for permitting the manufacture of sheathed electrical heating elements, which apparatus permits the mass production of such elements by means which can be more fully automated so that the production rate and efficiency can be substantially increased, while at the same time permitting heating elements to be manufactured with a high degree of consistency and uniformity.
It is also an object of this invention to provide an apparatus, as aforesaid, which utilizes an improved filling tube structure to facilitate the insertion and centering of the resistance conductor within the sheath, and which filling tube structure has an improved valve structure associated therewith to permit a more rapid filling of the sheath with insulating material.
Other objects and purposes of the invention will be apparent to persons familiar with apparatuses of this general type upon reading the following specification and inspecting the accompanying drawings.